A membrane contactor may be used for many purposes, including but not limited to, removing entrained gases from liquids, debubbling liquids, filtering liquids, and adding a gas to a liquid. Membrane contactors are known to be used in many different applications, for example, a membrane contactor may be used in removing entrained gases from inks used in printing.
Membrane contactors may also provide a means of accomplishing gas/liquid, and liquid/liquid (which can encompass liquid/dissolved solid) separations. Membrane contactors typically are used to bring two immiscible fluid phases—for example, a first liquid and a second liquid, or a gas and a liquid—into contact with one another to effect separation and/or transfer of one or more components from one fluid to the other.
A hollow fiber membrane contactor typically includes a bundle of microporous hollow fibers, and a rigid shell or housing enclosing the fiber bundle. The shell may be provided with four fluid ports: an inlet for introducing the first fluid, an outlet for discharging the first fluid, an inlet for introducing the second fluid, and an outlet for discharging the second fluid. The hollow fibers may be potted on both ends, within the housing, to form polymeric tube sheets with the fiber bores opening on each end into common first and second end cap portions of the shell. In a “tube-side” or “lumen-side” contactor, the first end cap may contain the inlet for the first fluid, which is designated the “tube-side” or “lumen-side” fluid because it is the fluid that passes through the internal lumens of the fibers. The second end cap contains the outlet for discharging the lumen-side fluid. The second fluid, designated the “shell-side” fluid, typically enters and exits the housing through inlet and outlet ports arranged between the tube sheets, whereby the shell-side fluid contacts the external surfaces of the fibers. The shell-side fluid flows through the interstices between fibers of the fiber bundle, and may be directed to flow parallel or perpendicular to the fiber length. As an example, U.S. Pat. No. 5,352,361 to Prasad, et al., incorporated by reference herein in its entirety, may assist in a background understanding of fluid contact across hollow fiber membranes within a shell.
In a “shell-side” contactor, the contactor may include a central core which passes through the end caps and has a first end serving as the inlet for the first fluid, which is designated the “shell-side” fluid because it is the fluid that passes over the exterior or shell of the hollow fibers. The first end cap may contain the inlet for the second fluid, which is designated the “tube-side” or “lumen-side” fluid because it is the fluid that passes through the internal lumens of the fibers. The second end cap contains the outlet for discharging the lumen-side fluid. The first fluid, designated the “shell-side” fluid, typically enters and exits the housing through inlet and outlet ports (open ends) of the perforated core, and typically exits and re-enters the perforations in the core between the tube sheets whereby the shell-side fluid contacts the external surfaces of the fibers. The shell-side fluid flows through the interstices between fibers of the fiber bundle, and may be directed to flow parallel or perpendicular to the fiber length.
Because the tube sheets separate the lumen-side fluid from the shell-side fluid, the lumen-side fluid does not mix with the shell-side fluid, and the only transfer between the lumen-side fluid and the shell-side fluid occurs through the walls of the hollow fibers. The fine pores in the fiber wall are normally filled with a stationary layer of one of the two fluids, the other fluid being excluded from the pores due to surface tension and/or pressure differential effects. Mass transfer and separation are usually caused by diffusion, which is driven by the difference in concentration of the transferring species between the two phases. Typically, no convective or bulk flow occurs across the membrane.
In the case of gas/liquid separations, membrane contactors are typically fabricated with hydrophobic hollow fiber microporous membranes. Since the membranes are hydrophobic and have very small pores, liquid will not easily pass through the pores. The membranes act as an inert support that brings the liquid and gas phases into direct contact, without dispersion. The mass transfer between the two phases is governed by the difference in partial pressure of the gas species being transferred.
For liquid systems, the liquid/liquid interface at each pore is typically immobilized by the appropriate selection of membrane and liquid phase pressures. In this case, the membrane also acts as an inert support to facilitate direct contacting of two immiscible phases without mixing.
Such known membrane contactors can be utilized for a variety of applications, including the separation of a component from a fluid or transferring a component of one fluid to another. For example, a membrane contactor can be used in removal of contaminants from an effluent stream. In many industrial processes, a contaminated effluent stream is generated as a by-product. In view of environmental concerns, and/or efforts to improve process efficiency, it is often desirable to remove one or more contaminants from the effluent stream so that the contaminant does not pollute the environment, negatively effect equipment, or so that it may be recycled. Existing industrial processes frequently must be upgraded to reduce environmental emissions and/or increase efficiency. Therefore, a need often arises for a process and system that can be economically retrofit to an existing plant to reduce emissions, protect equipment, recycle, or improve efficiency.
Several factors are important in the design of membrane contactors, including separation characteristics, cost, pressure drop, weight, and efficiency. The pressure drop across a contactor should be low to reduce the need for more expensive high pressure equipment. Low pressure drop is of particular importance in retrofit projects where a membrane contactor is to be added at the discharge point of an effluent process stream, as the process pressure at this point is typically at or near atmospheric pressure. High efficiency of mass transfer is desirable for reducing the size of the contactor. Low weight is desirable for decreasing installation and maintenance costs, and is of particular importance in offshore applications. At least certain existing membrane contactors have been found less than fully satisfactory in meeting these goals, for particular applications, for extreme conditions, or the like. For example, the shell portion of typical membrane contactors adds considerably to their weight and expense. Shell-type contactors also typically must operate at elevated pressures. Accordingly, a need exists for an improved membrane contactor having improved characteristics over known membrane contactors, for use in particular applications, for use in extreme conditions, or the like. It is to the provision of a microporous hollow fiber membrane device and/or method meeting these and/or other needs that at least selected embodiments of the present invention may be directed.
Baffled membrane contactors capable of separating fluids are known, for example, see U.S. Pat. Nos. 5,264,171; 5,352,361; and 5,938,922, each of which is incorporated herein by reference in its entirety. At least certain of such contactors may include a perforated center tube, a plurality of hollow fibers surrounding the tube, tube sheets affixing the ends of the hollow fibers, a baffle located between the tube sheets, and a shell surrounding the tube, fibers, tube sheets, and baffle. Other than as disclosed in the U.S. Pat. No. 5,938,922 patent, the fibers are usually open at the baffle so that there is fluid communication through the hollow fiber lumen from one tube sheet to the other. The U.S. Pat. No. 5,938,922 patent discloses having the fibers closed at the baffle to prevent fluid communication through the hollow fiber lumen near the midpoint of the fibers between the tube sheets.
Such contactors capable of separating fluids, for example, dissolved gas from water, have numerous industrial applications. Those applications include: rust prevention systems for boilers or power plant turbines; rust prevention systems for drinking water, cooling water, or hot water pipe lines; ultra-pure water sources for the electronics industry (e.g., rinsing semiconductor wafers during manufacture); ultrasonic cleaning processes; water sources for food processing; and the like.
Two of the foregoing applications are of particular interest. They are rust prevention in water pipe lines and ultra-pure water sources for the electronics industry. In each application, the removal of dissolved oxygen from water is extremely important. In rust prevention in water pipe lines, the oxygen reacts with dissolved iron or iron from the pipe line to form rust that may precipitate. In potable water, the rust precipitate is unattractive and causes staining; and in pipe lines, it can cause occlusion of the pipe. In ultra-pure water for the electronics industry, water is used to rinse semiconductor wafers during manufacture. Dissolved oxygen in the rinse water can etch the surface of the wafer and destroy it; it can also coat the wafer surface and prevent effective rinsing. Accordingly, the removal of dissolved gasses from water is extremely important.
Therefore, there is a need to develop new or improved contactors and systems for degassing of liquids.
Also, current designs of membrane contactors are effective for some applications, but may have certain issues or limitations related to, for example, the degassing of high flow rate liquids and/or high pressure liquids, such as seawater at about 50 gpm or more and/or about 300 psi, high pressure ratings, ASME code ratings, customer familiarity and acceptance, high cost, high weight, use of metal or other corrosive materials, modularity, replaceable self contained cartridges, porting options, module size, module array size, high pressure cartridges, excessively long fibers, liquid flow rates, gas concentration variation, do not allow for commercial production, and/or the like.
High flow rate, high pressure membrane contactors have long been the subject of interest to membrane developers. For example, selected gas transfer membrane contactors developed and manufactured by the Liqui-Cel business of Membrana-Charlotte a division of Celgard, LLC of Charlotte, N.C. can handle high flow rate (up to 400 gpm) and high pressure (up to 100 psi) liquids.
With the exception of the recent use of, for example, Liqui-Cel® Extra-Flow™ membrane contactor systems, most large scale industrial degasification systems still utilize very large vacuum towers to degasify water, seawater, and the like. For example, power plants and offshore oil rigs typically use large vacuum towers (30 feet tall or more) to degass water, process water, storage tank water, seawater, salt water, or the like.
A new or improved liquid degassing membrane contactor would allow for relatively small, modular, degassing modules to be used in industrial processes, at power plants, on offshore oil rigs or drilling platforms, to replace or augment vacuum towers, to provide the benefits of modularity and replaceable cartridges, and/or the like. Accordingly, there is a need for a new or an improved liquid degassing membrane contactor and methods of manufacture and/or use thereof, a new or improved high pressure liquid degassing membrane contactor and/or methods of manufacture and/or use thereof, a new or improved high pressure liquid degassing system, and/or the like.